The present invention relates generally to electrical connectors and jacks and, more particularly, to a jack adapted to be connected to a printed circuit board and a modular plug connector designed for use therewith.
The termination of multi-conductor cord by modular plug connectors has become commonplace. Examples of such modular plug connectors are disclosed in various patents, such as U.S. Pat. Nos. 3,699,498, 3,761,869, 3,860,316 and 3,954,320. Another advantageous configuration of a modular plug connector is disclosed in U.S. Pat. No. 4,211,462 assigned to Stewart Stamping Corporation, assignee of the instant application. Essentially, the modular plug connector includes a dielectric housing having a cavity into which an end portion of the cord is received. Flat contact terminals corresponding in number to the number of cord conductors are inserted into respective slots which open at one housing side and which are aligned with the conductors so that blade-like portions of the contact terminals pierce respective cord conductors. Straight upper edges of the contact terminals are exposed at the side of the housing in position for engagement by respective jack contacts when the modular plug connector is inserted into the jack.
It is becoming more commonplace to couple the conductors of a multi-conductor cord to the conductors of a printed circuit board through the use of a modular plug connector. Accordingly, jacks for modular plug connectors have been designed specifically for connection to printed circuit boards.
Conventional jacks of this type, such as those available from Virginia Plastics Company of Roanoke, Virginia, generally comprise a one-piece plastic housing having a longitudinal cavity adapted to receive the modular plug connector. Associated with the housing are a plurality of jack contacts adapted to engage the straight edges of the contact terminals of the plug connector when the latter is inserted into the jack receptacle. Each jack contact is held by slots or grooves formed in the jack housing and includes a portion which extends along the rear housing wall and projects below the bottom of the jack housing for insertion into the printed circuit board and a portion which extends through a slot formed through the jack housing top wall into the jack receptacle for engagement with the edge of a respective contact terminal of the plug connector.
Jacks of this type are not entirely satisfactory for several reasons. For example, the jack contacts are exposed externally of the jack both at the rear as well as at the top wall thereof thus subjecting the contacts to possible damage during use. Moreover, portions of the jack contacts tend to be pushed out or become loosened from the slots or grooves which hold them in place.
Conventional jacks for modular plug connectors designed for connection to printed circuit boards are not completely satisfactory for another important reason. Thus, digital-based electronic equipment is a major source of electromagnetic (EMI) and radio frequency (RFI) interference. Such interference has become a problem at least in part due to the movement away from metal and towards plastic as the material from which the plug connector housings are formed. Plastics generally lack the shielding capabilities which are inherent in metal housings.
In order to prevent or at least substantially reduce the emission of interference-causing electromagnetic and radio frequency radiation from multi-conductor cords used in digital-based electronic equipment and to provide at least some protection from interference-causing signals radiated from external equipment, cords have conventionally been provided with "shielding" in the form of a continuous sheath of conductive material between the outer insulation jacket of the cord and the insulated conductors, which sheath surrounds and encloses the conductors along their length. The shield can be formed of any suitable conductive material such, for example, as thin Mylar having a surface coated with aluminum foil or thin conductive filaments braided into a sheath construction. The shield acts to suppress or contain the interference-causing electromagnetic and radio frequency signals radiating outwardly from the cord conductors and, conversely, to prevent such high frequency signals generated by external equipment from causing interference in the conductors.
However, these techniques have not satisfactorily eliminated the interference problem and have created additional problems. Specifically, it has been found that there is still a tendency for EMI and RFI to result from the leakage of electromagnetic and radio frequency radiation signals from the cord in the region at which the modular plug connector is inserted into the jack receptacle. Moreover, it is not uncommon for high frequency signals radiated from nearby equipment to pass through the jack and cause interference in the cord conductors.
Furthermore, the radiation shield tends to acquire an electrostatic charge over a period of time and provisions therefore must be made to ground the shield. This has conventionally been accomplished either by means of a so-called "drain wire" which extends through the cord in electrical engagement with the conductive shield, the end of the drain wire passing out of the connector for connection to ground, or by grounding the shield through one of the modular plug connector contact terminals designed to engage a grounded jack contact upon insertion of the connector into the jack. However, when the radiation shield is grounded using such conventional techniques, it is not uncommon for deleterious electrical discharge arcs to occur across the connector contacts or across the printed circuit board conductors. Such arcing can cause serious damage to the electrical equipment.
The applicability of modular plug connections to digital-based electronic equipment, such as computers, has in the past been limited by the geometry of the electronic equipment and conventional plugs and jacks. Computers often include components consisting of a plurality of printed circuit boards stacked one over the other in closely spaced overlying relationship. For example, a computer may have printed circuit boards stacked one over the other with adjacent boards being spaced no more than one-half inch from each other. Since a typical printed circuit board has a thickness of about 0.060 inches and the pin portions of a jack connected to the board should protrude about 0.060 inches below the board bottom to permit effective soldering connections, an inter-board space of only about 3/8 inch would be available to accommodate a jack for receiving a plug connector. Indeed, this dimension may be even somewhat less where the jack is enclosed within an insulating sleeve to prevent electrical engagement with the jack pin portions protruding from the bottom of the next adjacent printed circuit board.
Since the height of conventional modular plug connectors is already about 3/8ths inch, the use of such connectors in environments of the type described above, keeping in mind the necessity of providing a jack for receiving the connector, is clearly not possible.
A modular plug connector and jack assembly is available from Amp Corp. under the designation Data Link wherein the outer surfaces of the plug receptacle entrance end of the jack is enclosed within a cap-like member of conductive sheet metal having contact projections which extend around the front of the jack and into the receptacle entrance. The cap-like member has pin portions adapted to be connected to ground through a printed circuit board. The connector housing is surrounded by a conductive collar which extends through the cord-receiving opening of the connector to terminate the cord shield. When the plug is inserted into the jack receptacle, the contact projections extending into the receptacle engage the shield terminating collar. This arrangement is not entirely satisfactory since the EMI/RFI shielding for the connector and the electrical engagement of the shield terminating collar of the connector to ground the same are not sufficient and reliable under all circumstances. Moreover, the location of the contact projections within the plug receptacle of the jack restricts the extent to which the profile of the jack can be reduced.
A jack for a modular plug connector adapted for connection to a printed circuit board is disclosed in applicant's copending application Ser. No. 612,722 filed May 21, 1984. Although the jack disclosed in said prior application provides effective shielding for the connector and grounding for shield-terminating structure of the connector, a more reliable shielding and grounding is always desired. Moreover, the jack disclosed in said prior application has a height which is too large to permit its use in the limited spaces described above.